The present disclosure relates to transparent glass-ceramic materials which contain a spinel solid solution as the main crystalline phase, corresponding precursor alumino-silicate glasses, articles made of said transparent glass-ceramic materials as well as a method for manufacturing such articles, and structures comprising a sheet made of such glass-ceramic materials and electronic or optoelectronic devices comprising such structures.
The transparent spinel glass-ceramics display a high transmission in the 400-1000 nm range and are environmentally friendly (free of arsenic and antimony). They are industrially obtained in an easy way insofar as their precursor alumino-silicate glasses show suitable liquidus (low temperature of liquidus and high viscosity at this temperature).
Some transparent spinel glass-ceramics also display interesting strain points and coefficient of thermal expansion. They are suitable substrates for high temperature growth of high quality monocrystalline or polycrystalline silicon thin films for example. Structures including such substrates with such thin films thereon can be used in photovoltaic devices, flat panel devices and liquid crystal devices.
Spinel glass-ceramics have been disclosed in numerous prior art documents.
U.S. Pat. No. 3,681,102 discloses transparent glass-ceramic articles comprising zinc spinel. The composition of the precursor glasses contains ZrO2 as a nucleating agent and, conventionally, a fining agent such as As2O3 may be included in the batch materials.
U.S. Pat. No. 4,687,750 relates to transparent glass-ceramics containing gahnite. The composition of the precursor glasses contains TiO2 as nucleating agent. Minor amounts of ZrO2 may be included in the composition without adversely affecting the properties of the crystallized products. Nonetheless it is explained that ZrO2 is unnecessary as a nucleating agent as TiO2 is a much more efficient nucleating agent. Moreover ZrO2 is much less soluble than TiO2 in the glass, hence its presence hazards unmelted particles and/or devitrification in the glass and requires higher melting temperature. To improve glass quality, a fining agent such as As2O3 and/or Sb2O3 may be added to the batch.
U.S. Pat. No. 5,476,821 describes high modulus glass-ceramics containing fine grained spinel-type crystals. Nucleation efficiency is enhanced by the presence of components such as TiO2, ZrO2 and NiO, and also high levels of Al2O3.
U.S. Pat. No. 5,968,857 describes transparent glass-ceramics containing spinel as a predominant crystal phase. The composition of the precursor glasses contains TiO2 and/or ZrO2 as nucleating agents. Fining agents such as As2O3 or Sb2O3 may be added to said precursor glass compositions.
L. R. Pinckney, the inventor of said U.S. Pat. No. 5,968,857, has also disclosed such transparent spinel glass-ceramics which display high strain point in the Journal of Non-Crystalline Solids, 255 (1999), pp. 171-177. The described glass-ceramics are able to withstand thermal treatments at 1000° C. without deformation. L. R. Pinckney has observed that precursor glasses melted with TiO2 (but without arsenic) leads to glass-ceramics showing a gray color and so having a low transmission in all the visible range. Such a low transmission is an impediment to the use of these glass-ceramics in photovoltaic applications and the like as it reduces the amount of light which is able to reach the silicon. L. R. Pinckney suggests that a partial reduction of titanium in Ti3+ is responsible for the very strong absorption in the visible. Actually, it appears that, in addition to its fining effect, arsenic also plays a role of bleaching agent.
U.S. Patent Application No. 2005/0096208 describes glass-ceramics containing spinel, sapphirine or cordierite as a main crystalline phase. Said glass-ceramics can be obtained in forming precursor glasses by the float method and then by ceramming the formed glasses. B2O3 is an essential component of the composition of the precursor glasses. P2O5, TiO2, ZrO2, SnO2 and Ta2O5 are proposed as nucleating agents. SnO2 is also proposed as fining agent.
WO Patent Application 2007/144875 also describes glass-ceramics containing spinel as a main crystalline phase. TiO2 is disclosed as a preferred nucleating agent. It may be used in a large amount.